Do you need a stem too? I'm pretty sure the style crown should of had the 'G' marking rather than 'Gruen'. Sorry to say I don't have one, but they are common on the swamp. Need to know the tap size too.

Don't want to be overly pedantic as I'm not familiar with your knowledge base.

All I know is based on hard work & writing by others. I can only aspire to augment this body of knowledge. If I am wrong it is because of my own failings. -me

"If I have seen farther it is by standing on the shoulders of giants." - Newton

first you need to know the movement used in this watch. Should be a 510 based variant already, I guess a 510R. BTW, your watch was born in 1962 and is known as "Mark". Stems should be easy to get, there are also pretty often a number of wrecked watches or movements in the swamp which might have stem and crown going with it.